Adjustable transformer



July 22, 1947.

J. A. ANDERSON ADJUSTABLE TRANSFORMER 2 Sheets-Sheet l Filed Jan. 9, 1945 ADJ US TABLE TRANSFORMER Filed Jan. -9, 1945 2 Sheets- Sheet 2 Patented July 22, 1947 UNITED STATES PATENT OFFICE ADJ USTABLE TRANSFORMER James A. Anderson, Memphis, Tenn.

Application January 9, 1945, Serial No. 571,974

4 Claims.

This invention relates to adjustable reactance transformers of the type used for welding and other purposes in which the electrical output of the secondary coil is controlled by means of a control of the magnetic flux.

Transformers of this type are usually either provided with a movable coil or with a magnetic shunt, but both methods as hitherto applied have inconveniences and drawbacks. To obtain a large variation of current in the case of a movable coil, a long track of the coil is necessary to obtain a small variation while in the case of a magnetic shunt, the control of output with most constructions presents the difliculty that excessively large and non-linear variations of the reactance result from certain displacements of the movable piece. Other constructions which have been proposed have the drawback already mentioned of requiring an excessive length of travel of the movable member for a required adjustment.

It is the object of this invention to provide means for controlling the output of an adjustable reactance transformer which avoid these difiiculties.

According to the invention, the transformer core is provided with a leg having a fixed air gap which is bridged by a movable flux-carrying bridge member of variable cross section. The magnetic flux through the air gap and thereby through the core carrying the coils is thus regulated by the adjustment of the cross section of the bridge piece which is adjusted according to the requirements.

Said magnetic flux, as well known, is propor tional to the number of magnetic lines of forces passing through the leg and through the cross section regulating the passage through its gap so that a finely adjustable control within practical limits is possible. This regulating arrangement permits to obtain a relatively wide range of reactance variations for a transformer of a given size.

A modification of the invention is illustrated in the accompanying drawings and is described in the following specification. It is, however, to be understood that the fact that merely one embodiment of the invention is described in specific terms is not to be considered as limitative. The

modification shown illustrates the basic idea by 1 taken along line 2--2 of Figure 1.

Figure 3 is a view of a horizontal section through the middle or center leg of the transformer, the section being taken along line 33 of Figure 1.

Figure 4 is a perspective view of the movable bridge piece.

The adjustable transformer comprises a laminated core 5 carrying the two coils 6, I, one of which forms the primary winding while the other form the secondary winding of the transformer. Between the two legs 8, 9 carrying the coils 6, I a middle or central leg I0 is arranged which is provided with a fixed air gap II. This leg is covered by shields l2 of non-magnetic material arranged on both sides of the leg l0 and fixed to it in any appropriate manner. These shields prevent the formation of stra magnetic fields through the parts and members mounted on the leg Ill. In the modification shown the shields are fastened to each other by means of screws 13 arranged above and below the transformer core 5.

The shields are provided with a stepped portion M for a purpose to be described.

Adjacent to the leg l0 and the air gap H is a movable leg member, generally indicated by the reference numeral l5 which consists of a body I6 of laminated magnetic material held by two clamping members I1. These clamping members I! are held by means of screw bolts l8 passing through them and through the movable leg member I6 and they are provided at their rear ends with inwardly projecting guiding flanges or ledges [9 which are sliding along the stepped portion [4 of the shields l2.

The movable leg member [6 is provided with a rear or guiding face 20 applied against the face of the leg HI and against the front ends of the shields 12 which are lying flush with the said face; the guiding portions [4 are holding the movable leg member [5 and provide a guideway for the same, along which it may slide.

Said movable leg member is provided with a wedge-like end portion 2| formed by an inclined surface as shown in Figures 2 and 4. This wedgelike portion furnishes varying cross sections through which the magnetic lines of force are passing on their way around the air gap H.

One of the clamping members I! is provided with a rack 22 at its front end which meshes with a pinion 23, carried by a shaft 24. The shaft runs transversely towards the panel board which is not shown and is provided at its end with a handle or crank or some other means for rotating it. It will thus be clear that rotation of the shaft 24 will rotate the pinion 23 and will lower or raise the rack together with the clampingmembers l! and the movable leg member I 6.

The function and operation of the parts will be clear from the following description. When the movable leg member is fully retracted on its uppermost position (as shown in the figures) the leg ID will have a substantial air gap offering a resistance which practically concentrates the magnetic flux on the legs 3 and 9, only a very small part of the magnetic flux produced by the primary coil being able to pass through the gap in leg [0.

When the movable leg member [5 bridges the air gap the magnetic lines of force may pass between the sections of le I!) separated by air gap l I to a varying extent. The extent to which such passage takes place depends on the smallest cross section of the shunt around the gap. On account of the wedge-like portion of the movable leg member, the cross section may be adjusted according to requirements by raising or lowering the movable leg member l5, whereby a smaller 01' larger section of the wedge 2! will act as a flux conductor in accordance with the position of the wedge member and with the wedge section applied against leg 20 corresponding to this position. The magnetic flux passing through leg will, therefore, vary in accordance with the position of leg member l and thereby a larger or smaller portion of the magnetic flux produced by the primary coil will be diverted through leg l0 and will fail to help in providing a current in the secondary.

Transformers of the type above described, provided with a fixed gap, bridged by a movable flux carrying bridge piece or leg member permit to adjust the smallest cross section of the permeable material through which the magnetic flux of the transformer leg, forming the magnetic shunt to the main legs, has to pass. The shifting of the bridge piece thus produces a fine adjustment of the magnetic reluctance in this leg. In addition, a further adjustment is possible by moving the bridge piece to such an extent that the thin edge portion of the wedge is no longer in contact with one of the le sections bordering the gap. This movement of the wedge-like bridge piece will permit to introduce an adjustable gap. It will thus be seen that a very wide range of adjustment is obtainable, the most important range section of which may show full linear proportionality between the adjustment made and the variation of the magnetic flux entailed by it, if desired.

It is also seen that the interdependence between the magnitude of the variation obtained and the adjustment to be made depends on the angle of inclination of the wedge-like face, which may be straight or curved, so as to conform itself to any desired relationship between these two adjustment factors.

The adjustable reactance transformer as described has a number of advantages over other constructions. As already stated, it provides means which can perform an adjustment entailing large variations of current without displacement of parts over a long track. On the other hand, it avoids non-linear and excessive current variations. A special advantage resides in the fact that the primary coil need not any longer be tapped or provided with a contactor arrangement to change the ratio of translation between the windings of the primary and those of the secondary coil. The adjustment of the transformer therefore simplifies the transformer construction.

It may finally be mentioned that transformers with variable or adjustable reactance are useful in several fields, the most important field being that of the welding machine, supplying current of high amperage to the welding arcs. The present invention is, therefore, most useful in this field although the invention itself is not related and not limited to any specific use as it is mainly concerned with the means for adjusting the reactance of the transformer itself, and not with the specific application of such an adjustable transformer.

What I claim is:

1. An adjustable reactance transformer of the character described comprising a core carrying windings, a transformer leg forming a magnetic shunt to the winding carrying core consisting of two sections, separated by a fixed air gap, a further movable flux carrying leg member of magnetic material provided with a tapering section, movable alongside both leg sections and bridging the gap between the same during such movement, and means for adjusting the position of the tapering section for varying the cross section of the permeable flux carrying material for the passage of the magnetic flux.

2. An adjustable reactance transformer of the character described comprising a core carrying windings, a transformer leg forming a magnetic shunt to the winding carrying core and consisting of two leg sections separated by a fixed air gap, 2, further flux carrying leg member with a wedge shaped section, bridging said gap and adapted to be moved alongside said divided transformer leg in contact with both leg sections, for adjusting the cross section of the magnetically permeable flux carrying material across the gap and further adapted to be moved along one leg section out of contact with the other section in order to provide an adjustable gap Within the fixed gap.

3. An adjustable reactance transformer of the character described comprising a core carrying windings, a transformer leg forming a magnetic shunt to said core and consisting of two leg sections, separated by a fixed transverse air gap, a further flux carrying leg member with a wedge shaped end section bridging said gap and adapted to be moved alongside said separate leg sections, means for moving said leg member in substantial parallelism with leg sections across said gap and through said gap, said means comprising clamping plates of non-magnetic material arranged along one leg section, for gripping, holding and guiding said flux carrying leg member, and means including hand-operated members, and a rack and pinion transmission for moving said leg memher along the aforesaid leg section between the clamping plates.

4. An adjustable reactance transformer of the character described comprising a core carrying transformer windings and forming a magnetic circuit, a magnetic shunt circuit including two separate members of magnetic material, projecting from the said circuit forming core, a movable and adjustable leg member provided with a varying cros section, movable alongside of and in magnetic contact with flux carrying surfaces of the said projecting members and presenting portions of variable cross section to at least one of w the said flux carrying surfaces of the projecting members of the shunt circuit for adjusting the JAMES A. ANDERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Thordarson May 17, 1921 Number 

